MD5

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MD5
Documentation
#include <cryptopp/md5.h>

MD5 is a message digest created by Ron Rivest in 1992. MD5 is no longer considered secure, and you should use a modern hash like BLAKE2, Keccak, SHA2, or SHA3. You should only use MD5 if you are interoping with legacy systems.

MD5 is declared in the Weak namespace. You must define CRYPTOPP_ENABLE_NAMESPACE_WEAK before you include MD5 header file or use MD5. You must also declare variables in the weak namespace using Weak::MD5.

All Crypto++ hashes derive from HashTransformation. The base class provides functions like Update, Final and Verify. You can swap-in any hash for any other hash in your program.

Sample Programs

There are five sample programs. The first prints information about the hash. The second creates a hash using MD5 class. The third creates a hash using a pipeline. The fourth and filth examples show how to verify an existing digest.

The examples below use MD5, but you can swap-in any hash function, like PanamaHash or SM3. Notice the sample program defines CRYPTOPP_ENABLE_NAMESPACE_WEAK before including md5.h. Also notice the hash variable is declared Weak::MD5.

The first example dumps the name, digest size and internal block size of the hash.

#include "cryptlib.h"

#define CRYPTOPP_ENABLE_NAMESPACE_WEAK 1
#include "md5.h"

#include <iostream>

int main (int argc, char* argv[])
{
    using namespace CryptoPP;

    Weak::MD5 hash;	
    std::cout << "Name: " << hash.AlgorithmName() << std::endl;
    std::cout << "Digest size: " << hash.DigestSize() << std::endl;
    std::cout << "Block size: " << hash.BlockSize() << std::endl;

    return 0; 
}

Running the program results in the following. In general you should use DigestSize and avoid BlockSize. BlockSize is usually not required by a program.

$ ./test.exe
Name: MD5
Digest size: 16
Block size: 64

The second example creates a hash using the hash object and member functions. You add data using Update and you calculate the hash using Final. Calling Final resets the hash so you don't need to do it manually.

using namespace CryptoPP;
HexEncoder encoder(new FileSink(std::cout));

std::string msg = "Yoda said, Do or do not. There is no try.";
std::string digest;

Weak::MD5 hash;
hash.Update((const byte*)msg.data(), msg.size());
digest.resize(hash.DigestSize());
hash.Final((byte*)&digest[0]);

std::cout << "Message: " << msg << std::endl;

std::cout << "Digest: ";
StringSource(digest, true, new Redirector(encoder));
std::cout << std::endl;

Running the program results in the following.

$ ./test.exe
Message: Yoda said, Do or do not. There is no try.
Digest: CF4A16604182539B5CE297092A034625

You can also obtain a truncated hash rather than the full hash using TruncatedFinal.

std::cout << "Message: " << msg << std::endl;

hash.Update((const byte*)msg.data(), msg.size());
digest.resize(hash.DigestSize()/2);
hash.TruncatedFinal((byte*)&digest[0], digest.size());

std::cout << "Digest: ";
StringSource(digest, true, new Redirector(encoder));
std::cout << std::endl;

The program produces the following result.

$ ./test.exe
Message: Yoda said, Do or do not. There is no try.
Digest: CF4A16604182539B

Using a pipeline produces the same result. It relieves you of calling Update and Final manually. The code also uses a HashFilter, which has its own wiki page at HashFilter.

std::string msg = "Yoda said, Do or do not. There is no try.";
std::string digest;

StringSource(msg, true, new HashFilter(hash, new StringSink(digest)));

std::cout << "Message: " << msg << std::endl;

std::cout << "Digest: ";
StringSource(digest, true, new Redirector(encoder));
std::cout << std::endl;

Running the program results in the following.

$ ./test.exe
Message: Yoda said, Do or do not. There is no try.
Digest: CF4A16604182539B5CE297092A034625

The fourth program verifies an existing hash using the hash object. Notice the program proceeds as if the hash is going to be calculated. But rather than calling Final to retrieve the hash, Verify is called to verify the existing hash.

Weak::MD5 hash;
hash.Update((const byte*)msg.data(), msg.size());
bool verified = hash.Verify((const byte*)digest.data());

if (verified == true)
    std::cout << "Verified hash over message" << std::endl;
else
    std::cout << "Failed to verify hash over message" << std::endl;

The final program verifies an existing hash using a pipeline. The code uses a HashVerificationFilter, which has its own wiki page at HashVerificationFilter.

bool result;
StringSource(digest+msg, true, new HashVerificationFilter(hash,
                 new ArraySink((byte*)&result, sizeof(result))));

if (result == true)
    std::cout << "Verified hash over message" << std::endl;
else
    std::cout << "Failed to verify hash over message" << std::endl;

Running the program results in the following output.

$ ./test.exe
Message: Yoda said, Do or do not. There is no try.
Digest: CF4A16604182539B5CE297092A034625
Verified hash over message

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